Advances in understanding Alzheimer's disease (AD) have partially clarified the composition of 2 major lesions in the AD brain, i.e. amyloid rich senile plaques (Sps) and neurofibrillary abnormalities including neurofibrillary tangles (NFTs), dystrophic plaque-associated neurites and neuropil threads (NTs). Specifically, the filamentous components in Sps assemble from incompletely degraded Beta-amyloid or A4 peptides (BetaA4) derived from 1 or more of 3 major amyloid precusor proteins (APPs) in brain (i.e. APP695, APP751 and APP770) while the paired helical filaments (PHFs) in NFTs, dystrophic plaque neurites and Nts are abnormally phosphorylated tau derivatives (known as PHFtau or A680. Although recently identified mutations in the APP gene may play a role in the etiology of AD in a small subset of patients with familial AD (FAD), increasing evidence suggests that AD results from the abnormal metabolism of APPs and tau. This has prompted efforts to establish models of AD pathology in mice bearing BetaA4 containing partial or complete APP transgenes, and in rats injected with BetaA4 or SP cores. However, the development of additional animal models that more closely mimick AD is critical for elucidating the etiology and pathogenesis of AD. To this end, the goal of Project #4 is to establish alternative models of AD pathology in rodents. To probe the biology of PHFs and their interactions with BetaA4 in vivo, we will extend recent work from our lab in which A68 proteins were injected into rat brains and induced long lived co-deposits of rodent BetaA4 at the injections site. Additionally, we will probe the in vivo generation of BetaA4 in rodents transplanted with cultured human neurons (NT2N cells derived from the NT2 cell line) that constitutively secrete BetaA4 and express APP695 almost to the exclusion of APP751/770. Studies also will be conducted on transplants of transfected NT2N cells that over express APP695 or APP751 with and without a FAD mutation. The injected A68 proteins and grafts of the NT2N human neurons will be introduced into regions of the rodent brain that are homologous with regions of the human AD brain that accumulate abundant (hippocampus) or negligible (cerebellum) amyloid and neurofibrillary lesions. The analysis of injected A68 and NT2N grafts will be carried out at post- operation survival times of days to 24 months using biochemical methods as well as by immunohistochemistry in conjunction with light, confocal an electron microscopy. These strategies to model major AD lesions in the rodent brain should lead to significant new insights into the pathogenesis of AD.